1. Field of Invention
The present invention relates to natural gamma ray logging in well boreholes.
2. Description of Prior Art
Prior efforts, such as in U.S. Pat. Nos. 3,940,610 and 3,976,878 have used natural gamma ray logging to measure the content of thorium, uranium and potassium (or daughter products of these elements) of earth formations adjacent well boreholes for study of characteristics of the formation. It was recognized that the measurement of uranium gamma ray energy at a window or energy range containing the 1.76 MeV uranium gamma ray energy peak was affected by gamma radiation from thorium in the formation, while the measurement of potassium gamma ray energy at a window containing the 1.46 MeV potassium gamma ray energy peak was affected by gamma radiation from both thorium and uranium in the formation. To compensate for this, factors known as stripping constants were obtained from measurements taken from test formation samples of known elemental concentrations. The stripping constants so obtained were then used to correct the natural gamma radiation counts obtained in earth formations for the effect of radiation from one element on measurements of radiation from other elements.